(Optional) Configuring VRRP Stability Functions

To help a VRRP group work stably, enable the preemption function, set a preemption delay, and specify an interval at which VRRP Advertisement packets are sent. The configuration can minimize impact of network flapping resulted from frequent master/backup VRRP switchovers on data forwarding.

Context

A VRRP group performs a master/backup switchover if the master device fails or a network is busy. After the master device or network communication recovers, a new master device is selected.

If a network flaps, service packets are adversely affected. VRRP stability functions can be configured to improve VRRP stability, minimizing network interruptions or packet loss resulted from frequent master/backup VRRP switchovers. Table 1 describes VRRP stability functions.

**Table 1** VRRP stability functions
Basic Function	Description
Setting a preemption delay	Frequent master/backup switchovers on an unstable network may cause double master devices to coexist or hosts to learn incorrect master MAC address. To maintain the stable master/backup status, configure either of the following preemption modes: Immediate preemption: A backup device immediately preempts the Master state after the master device fails. The preemption delay is 0s. This setting minimizes the service interruption time. Delayed preemption: The master device preempts the Master state a specified preemption delay after the master device recovers. During the preemption delay, other services (such as route convergence) are restored. The preemption delay helps minimize packet loss ratios.
Setting the interval at which VRRP Advertisement packets are sent	Heavy network traffic or timer setting differences between devices may cause a backup device to incorrectly preempt the Master state. To prevent this issue, set a large value for the interval at which VRRP Advertisement packets are sent by the master device.
Setting a recovery delay	If a VRRP-enabled interface status changes frequently, the VRRP status on the interface frequently alternates between Up and Down. To prevent this issue, set a recovery delay. A VRRP group responds to a VRRP interface Up event only after a specified recovery delay. The recovery delay helps prevent VRRP status flapping caused by frequent interface status changes.

Procedure

Set a preemption delay for a device in a VRRP group.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run vrrp vrid virtual-router-id preempt-mode timer delay delay-value
  A preemption delay is set for the device in a VRRP group.
  
  You can run the vrrp vrid virtual-router-id preempt-mode disable command to configure the non-preemption mode for devices in a VRRP group. When a VRRP group works in non-preemption mode, another backup device cannot preempt the Master state so long as the master device is working properly.
  
  A preemption delay is a period of time during which a backup device waits to preempt the Master state. When an IP address owner recovers from a fault, it immediately preempts the Master state. Therefore, the preemption delay is meaningless for an IP address owner. If a preemption delay needs to be configured for a VRRP group, do not configure the master device in the group as an IP address owner.
4. Run commit
  The configuration is committed.
Set an interval at which VRRP Advertisement packets are sent.
1. Run system-view
  The system view is displayed.
2. Run vrrp timer-advertise learning enable
  The device is enabled to learn the interval at which VRRP Advertisement packets are sent.
  
  During a master/backup VRRP switchover, do not disable the device from learning the interval. Otherwise, two master devices may coexist.
3. Run interface interface-type interface-number
  The view of the interface on which the VRRP group is configured is displayed.
4. Run vrrp vrid virtual-router-id timer advertise advertise-interval
  An interval at which VRRP Advertisement packets are sent is set.
  
  Run vrrp vrid virtual-router-id timer advertise millisecond millisecond-interval
  
  A millisecond interval at which VRRP Advertisement packets are sent is set.
5. Run commit
  The configuration is committed.
Set a recovery delay.
1. Run system-view
  The system view is displayed.
2. (Optional) Run interface interface-type interface-number
  The view of the interface on which the VRRP group is configured is displayed.
3. Run vrrp recover-delay delay-value
  A recovery delay is set.
  
  The vrrp recover-delay command run in the system view takes effect on all VRRP groups on the same device.
  
  The vrrp recover-delay command run in the interface view takes effect on all VRRP groups on the same interface. If the vrrp recover-delay command is run in both the system and interface views, the setting in the interface view prefers.
4. Run commit
  The configuration is committed.